Bioplastic using a plant as a raw material can contribute to a countermeasure against petroleum depletion and global warming and has been started being used not only in common products such as packaging, containers and fibers but also in durable products such as electronics and automobiles.
However, general bioplastics, such as polylactic acid, polyhydroxyalkanoate and modified starch, all use starch materials, more precisely, edible parts, as raw materials. Accordingly, for fear of future food shortage, it has been desired to develop a novel bioplastic using a non-edible part as a raw material.
As a raw material of a non-edible part, cellulose which is a main component of wood and plant is representative, and various types of bioplastics using the cellulose have been already developed and commercialized.
However, since a step of chemically modifying cellulose to obtain a resin is complicated and laborious and much energy is required for production, manufacturing cost of a cellulose resin is high. In addition, since durability (strength, heat resistance, water resistance, etc.) of a produced resin is not sufficient, use of the resin is limited.
Cellulose is produced as pulp by chemically separating lignin and hemicellulose from wood, etc., with the help of a chemical agent. In contrast, cotton can be used as it is since it is virtually formed of cellulose. Such a cellulose, which is a high molecular weight compound formed by polymerization of n-glucose, has a large number of hydroxy groups and thus has strong intermolecular force due to hydrogen bonds. Because of this, cellulose is hard and fragile, and has no thermoplasticity and a low solubility in a solvent except a special solvent. In addition, due to a large number of hydrophilic hydroxy groups, water absorbability is high and water resistance is low.
For improving such properties of a cellulose, various investigations have been made.
As a method for improving the properties of a cellulose, a method of substituting a hydrogen atom of a hydroxy group in a cellulose with a short-chain acyl group such as an acetyl group is known. According to this method, since the number of hydroxy groups can be reduced, the intermolecular force of a cellulose can be reduced. A further investigation has been made for producing a cellulose derivative having satisfactory thermoplasticity and water resistance by introducing a long-chain organic group having a larger number of carbon atoms in addition to a short-chain acyl group such as an acetyl group.
For example, Patent Literature 1 describes a cellulose derivative produced by substituting at least a part of hydrogen atoms of hydroxy groups of a cellulose with a short-chain acyl group (for example, an aliphatic acyl group having 2 to 4 carbon atoms) and a long-chain acyl group (for example, an aliphatic acyl group having 5 to 20 carbon atoms), and that the cellulose derivative has a low water absorption rate, satisfactory thermoplasticity, strength and fracture elongation and is suitable for molding process.
Patent Literature 2 describes a cellulose derivative having cardanol introduced therein, and that the cellulose derivative was improved in thermoplasticity, mechanical characteristics and water resistance.
Patent Literature 3 describes a cellulose derivative having cardanol and abietic acid introduced therein, and that the cellulose derivative was improved in thermoplasticity, mechanical characteristics and water resistance.